Punch construction



May 20, 1969 WQROEHRS PUNCH CONSTRUCTION Sheet Filed Jan. 19, 1966 INVENTOR. I 6060/0 11/ fvfirs A T TOPNE Y May 20, 1969 e. w. RoEHRs 3,444,719

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ZQ fiw TORNE Y United States Patent 3,444,719 PUNCH CONSTRUCTION Guenter W. Roehrs, Rochester, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Jan. 19, 1966, Ser. No. 521,627 Int. Cl. B21i 13/00; B21c 3/16; B2111 22/00 U.S. Cl. 72-462 4 Claims ABSTRACT OF THE DISCLOSURE A punch for deforming metal in which the active portion of the punch is made up of a plurality of filler elements. The punch construction improves fatigue life and reduces maintenance.

My invention relates generally to metal forming and more specifically to punch type components for cold metal forming and forging dies. In most cases, punches are the most wear susceptible parts of the metal forming tools and cause the major part of the maintenance, replacement and down time costs.

My invention is directed toward providing construction of a component with superior properties, particularly improved fatigue life, to reduce maintenance, replacement and down time costs thereby improving the economy of manufacturing processes utilizing conventional present day punch designs. I have generally accomplished this by providing a multipiece punch construction rather than the conventional one-piece solid type punch construction.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description of preferred embodiments of the invention as illustrated in the accompanying sheets of drawings in which:

FIGURE 1 is a cross section of a typical die set provided with a punch in accordance with a first embodiment of my invention.

FIGURE 2 is a section taken along the line 22 of FIGURE 1 and looking in the direction of the arrows.

FIGURE 3 is an elevation partially in cross section of a punch in accordance with a second embodiment of my invention.

FIGURE 4 is a section taken along the line 4-4 of FIGURE 3 and looking in the direction of the arrows.

FIGURE 5 is an elevation partially in cross section of a punch in accordance with a third embodiment of my invention.

Referring now to the drawings in detail and more particularly to FIGURE 1, I have shown a die set indicated generally at 12 for use with a press (not shown) with the parts thereof in their position at the end of the press stroke. The press comprises a ram (not shown) movable toward and away from a fixed bed (not shown). A die insert 18 is mounted on the fixed bed by retainer ring 17 bolted at 19 to the lower die shoe 16. The die 18 is representative of any type of die which may be used in conjunction with a punch type component of metal forming. As illustrated, the die 18 comprises a number of concentric rings 20 secured together at their upper end by a ring 22 which is threaded onto the outer diameter of the outer ring 20. The die 18 illustrated is adapted to form a head and extrude a shank on a workpiece indicated at 24. The head is formed by the punch 26 which is admitted to the die chamber through an opening 28 in the ring 22.

The punch 26 comprises an adapter 29 secured to the movable upper assembly by a retainer ring 14. The lower portion 30 of the adapter 29 is tubular and has a radially inwardly extending flange 32. The punch 26, consisting 3,444,719 Patented May 20, 1969 "ice of shell 34, two concentric sleeves 44 and the center pin 42 is inserted into the tubular portion 30 of the adapter 29 and held in position by a plug 40 which urges the frusto-conical shoulder 38 into engagement with a mating shoulder on the tubular portion 30. The stub pin 42 is coaxial and coextensive with the shell 34. As illustrated, two concentric annular elements 44 are nested within the annular space between the shell 34 and the stub pin 42. While I have only illustrated two such annular elements, the number could obviously be increased or decreased to suit a particular design. The elements 44 are also coextensive with the shell 34 so that the lower end walls of the shell 34, the annular elements 44, and stub pin 42 present a continuous surface 45. The surface 45 is the work contacting surface which forms the head on workpiece 24.

A collar 46 is mounted on a number of circumferential shoulder screws 48 threaded to the adapter 29. The collar 46 surrounds the tubular portion 30 of the adapter 29 and is movable axially with respect to it. It includes an inner cupped surface 47 adapted to engage the upper portion of the ring 22 to provide accurate alignment between the punch assembly 26 and the die 18. Coil springs 50 surround each shoulder screw 48 and bias the collar 46 downwardly. The operation of the press should be obvious. At the beginning of the press stroke, the ram is up and the collar 46 is extended by the springs 50 until it abuts the shoulders on the screws 48. As the movable ram head moves downwardly toward the bed and die 18, the collar 46 engages the upper ring 22 on the die 18 to align the punch 26 with the die 18. As the head moves further downward the lower end of punch 26 protrudes into the die cavity via the opening 28 to form the workpiece 24. During this downward movement, the collar 46 moves axially with respect to the head and adapter 29 storing energy in springs 50. As the ram head reverses direction to withdraw punch 26 from the die cavity, the energy in springs 50 returns collar 46 to its initial position at the start of the press stroke.

The following advantages of the first embodiment of my multipiece punch construction are to be noted. Because of the multipiece construction, the forging temperatures on the workpiece will not cause heat check cracks on the punch. The elements of the punch assembly expand freely under the influence of the contact heat without heat check cracks. The first embodiment as illustrated in FIGURE 1 thus is especially suitable for hot forming operations. The multipiece punch assembly also has a. greater unit strength because, in general, smaller parts are stronger per square inch than larger ones. Likewise, the individual smaller parts will have a better response to heat treatment resulting in superior quality and strength.

Another advantage is that metals with different physical properties may be used in the individual parts or elements to match the requirements of the parts of the piece being formed. The resulting punch assembly has a larger capacity for bending forces because its section modulus is increased. The distribution of operating stresses is more uniform in the multipiece punch resulting in reduced stress concentration and increased elastic deformation making the multipiece punch assembly superior with respect to fatigue failure.

Referring now to FIGURE 3, I have illustrated a second embodiment of my invention. In this embodiment, the adapter 128 has a retainer unit 130 threaded to it. The retainer nut 130 has an inwardly extending flange 132 providing an upper shoulder which abuts the lower surface of an outwardly extending flange 134 on the punch shell 136. The lower end 129 of the adapter 128 extends slightly into the shell 136 and closes its upper end. The shell 136 tapers from its upper end to a portion 138 of constant diameter. The tapered portion is filled by a number of backup plates 140 having tapered circumferential walls. The hollow portion 138 of constant diameter is filled with a number of flat circumferential discs 142 which are coaxial with the shell 136. The discs 142 are stacked one upon another and together with the backup plates completely fill the shell 136. A Work contacting nose 144 is threaded t the lower end of the shell 138. The nose 144 illustrated in FIGURE 3 has a tapered work contacting surface 146.

A third embodiment of my invention is shown in FIG- URE 5. It differs from the embodiments shown in FIG- URES 3 and 4 mainly in that the outer cylindrical shell 138 has been replaced by a central tie rod 238 having a nut 229 threaded to its upper end and resting on shoulders 230 or adapter 228. The work contacting nose 244 which, in this instance, is shown as having a flat work contacting surface 246 is secured to the lower end of the tie bolt 238. The circular discs 242 have central holes so that they surround the tie bolt 238 and are sandwiched between the nose 244 and the adapter 228. The discs 242 are thus axially fixed and restrained from lateral movement by the tie bolt 238 which was the function of shell 138 in the previous embodiment.

The embodiments shown in FIGURES 3, 4, and 5 are especially suitable for cold forming operations. This is because the discs have a higher compressive punch strength because of the favorable ratio of'cross sectional area to thickness. Again, the small size of the parts is more adaptable to heat treatment.

Friction developed between each fiat contact surface of the discs 142 acts against upsetting and reduces detrimental shear stress set up in the punch under its operating load. This type friction and its favorable effect is increased by alternate use of different discs from materials having different values for their modulus of elasticity; for instance, a punch nose from carbide is backed up by a disc from hardened steel, which is backed by a disc from carbide, which is backed up by a steel disc again, and so on.

The enclosure of the discs 142 by shell 136 acts also as resistance against upsetting of the assembly by restricting lateral expansion of the discs and therefore the growth of detrimental shear stresses.

Another advantage of the embodiments of FIGURES 3, 4 and 5 is in the throwaway type punch nose which allows economic salvage of the punches after wear on the punch nose.

Various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the appended claims as only preferred embodiments thereof have been disclosed.

I claim:

1. A punch for deforming metal comprising, in combination, an outer cylindrical shell having a longitudinal central axis, a work contacting nose mounted at one end of said shell, means to close the other end of said shell, and a plurality of filler elements disposed within said shell coaxially with said longitudinal axis, each of said elements having a transverse contour similar to the inner transverse contour of said shell, said filler elements including flat cylindrical discs stacked within said outer cylindrical shell, whereby a multipiece solid cylindrical punch is formed.

2. The punch as defined in claim 1 wherein said included discs and said work contacting nose are circular.

3. The punch as defined in claim 1 wherein said included discs and said cylindrical nose are alternately of a first and second material, said materials having different moduli of elasticity.

4. The punch as defined in claim 2 wherein said included discs and said circular nose are alternately made from steel and carbide.

References Cited UNITED STATES PATENTS 560,515 5/1896 Mason 72481 581,875 5/1897 Woods 72478 1,449,385 3/ 1923 Dieterich 72360 1,458,294 6/1923 Hook 72354 2,688,793 9/ 1954 Carlson 29--597 2,738,575 3/ 1956 Swain 72354 FOREIGN PATENTS 1,042,354 10/1958 Gernmay.

CHARLES W. LANHAM, Primary Examiner.

G. P. CROSBY, Assistant Examiner.

U.S. Cl. X.R. 72352, 476

Patent No. 3,444,719

May 20 Guenter W. Roehrs s in the above identified It is certified that error appear hereby corrected as patent and that said Letters Patent are shown below:

line 59, "of should read for Column 2 line 66,

Column 1,

Column 3, line l7, "or" should read of should read nut Signed and sealed this 14th day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer "unit" WILLIAM E. SCHUYLER, JR.

Commissioner of Patents 

